Vitamin D 3 (LH) complexes with manganese(II), iron(II), iron(III) and zinc(II) were identified in water-ethanol medium (30/70). Their stability constants were determined at 298 K and at a constant ionic strength of 0.100 M using potentiometric methods. The computerisation of the experimental data showed the presence of ML (M =metal, L=deprotonated vitamin D3) and ML2 species in all cases; in addition, the ML3 iron(Ill) complex was detected. The calculated overall stability constants /3 for Mn"L, FenL, FeI'L and ZnUL are, respectively, in logarithms, 12.4, 16.5, 28.5 and 16.5. Under the experimental conditions, the only protonated species MLH detected was with iron (III).